A transparent cache for datastore, backed by memcache.

service/datastore/properties.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 import (
         "errors"
         "fmt"
         "math"
@@ skipping 396 matching lines @@
 }
 
 // Save implements PropertyLoadSaver.Save by returning a copy of the
 // current map data.
 func (pm PropertyMap) Save(withMeta bool) (PropertyMap, error) {
         if len(pm) == 0 {
                 return PropertyMap{}, nil
         }
         ret := make(PropertyMap, len(pm))
         for k, v := range pm {
-                if withMeta || len(k) == 0 || k[0] != '$' {
+                if withMeta || !isMetaKey(k) {
                         ret[k] = append(ret[k], v...)
                 }
         }
         return ret, nil
 }
 
 // GetMeta implements PropertyLoadSaver.GetMeta, and returns the current value
 // associated with the metadata key. It may return ErrMetaFieldUnset if the
 // key doesn't exist.
 func (pm PropertyMap) GetMeta(key string) (interface{}, error) {
@@ skipping 15 matching lines @@
                 return err
         }
         pm["$"+key] = []Property{prop}
         return nil
 }
 
 // Problem implements PropertyLoadSaver.Problem. It ALWAYS returns nil.
 func (pm PropertyMap) Problem() error {
         return nil
 }
+
+// DataLen returns the number of non-metadata rows in this PropertyMap.
+func (pm PropertyMap) DataLen() int {
+        ret := 0
+        for k := range pm {
+                if isMetaKey(k) {
+                        continue
+                }
+                ret++
+        }
+        return ret
+}
+
+func isMetaKey(k string) bool {
+        // empty counts as a metakey since it's not a valid data key, but it's
+        // not really a valid metakey either.
+        return k == "" || k[0] == '$'
+}